chore(nimbus): ComboBox unit tests and bugfixes (#818)

* chore(nimbus): combobox - layout structure tests

* chore(nimbus): combobox - multi-select tag display tests

* chore(nimbus): combobox - input field behavior tests

* chore(nimbus): combobox - button visibility and behavior tests

* chore(nimbus): combobox - focus behavior tests

* chore(nimbus): notes

* chore(nimbus): combobox - keyboard navigation tests

* chore(nimbus): combobox - menu opening and closing tests

* chore(nimbus): combobox - option selection tests

* chore(nimbus): combobox - clear button functionality tests

* chore(nimbus): combobox - multi and single select behavior tests

* chore(nimbus): combobox - selection persistence tests

* chore(nimbus): combobox - basic text filtering tests

* chore(nimbus): combobox - custom filter tests

* chore(nimbus): combobox - empty state handling tests

* chore(nimbus): combobox - basic custom option creation tests

* chore(nimbus): combobox - single select creation tests

* chore(nimbus): combobox - a11y keyboard tests

* chore(nimbus): combobox - a11y relationship tests

* chore(nimbus): combobox - visual variant tests

* chore(nimbus): combobox - state visual tests

* chore(docs): remove temporary testing plan file

* chore(combobox): revisions

* feat(combobox option): options in listbox don't focus on hover

* chore(combobox): add test for modal integration

* chore(dialog): squelch button context for children

* Revert "chore(dialog): squelch button context for children"

This reverts commit af7f799.

* chore(combobox): edit tests after rebase

* chore(combobox): await in test, fix

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Co-authored-by: Byron Wall <byron.wall@commercetools.com>

Author: jaikamat